Dresden 2014 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 54: Correlated Electrons: Heavy Fermions

TT 54.6: Vortrag

Mittwoch, 2. April 2014, 10:45–11:00, HSZ 204

XMCD-Signatures of Kondo and Heavy Fermion Behaviour in the Surface Intermetallic CePt₅/Pt(111) — Christian Praetorius, •Martin Zinner, and Kai Fauth — Physikalisches Institut, Universität Würzburg, Am Hubland, D-97074 Würzburg

In this contribution, we explore the detection of magnetic signatures of Kondo and heavy fermion physics by x-ray spectroscopy and study the anisotropic paramagnetic Ce-4f response in CePt₅, prepared on Pt(111). Qualitatively, the magnetic behaviour above T 20 K is readily understood in terms of a hexagonal crystal field (CF), acting on weakly interacting, considerably screened Ce-4f moments. A quantitative description necessitates distinct CF parameters for ‘inner’ and ‘surface’ atomic layers. This approach is strongly supported by complementary structural information (LEED-IV). Treating both CF and Kondo physics within a simplified NCA approach [1] proved unsuccessful and we therefore resort to a more ad-hoc kind of Hamiltonian.

The paramagnetic response displays an anomaly (T^* ≈ 18 K), which we shall discuss as signalling the transition towards the coherent heavy fermion state . Well below T^* we find Ce 4f saturation moments much smaller than the free ion values. Their occurrence, too, can be understood to be characteristic of the coherent state and associated with a Lifshitz transition as predicted theoretically [2]. X-ray spectroscopy thus proves valuable for investigating strongly correlated electron systems in case sufficiently well-defined surfaces can be obtained.

[1] G. Zwicknagl, V. Zevin und P. Fulde, Z. Phys. B 79, 365 (1990)

[2] K. S. D. Beach and F. F. Assaad, Phys. Rev. B 77, 205123 (2008)